This application claims the priority of the commonly owned German patent application Serial No. 199 11 332.7 filed Mar. 15, 1999 and of the International patent application Serial No. PCT/DE00/00800 filed Mar. 13, 2000. The disclosures of the above-referenced priority applications, as well as that of each U.S. and foreign patent and patent application identified in the specification of the present application, is incorporated herein by reference.
The present invention relates to improvements in power trains for motor vehicles. More particularly, the invention relates to improvements in means for automatically controlling or regulating the operation of a component (such as the friction clutch) which, when engaged, is arranged to transmit torque between the rotary output element of a prime mover (such as the camshaft or the crankshaft of an internal combustion engine) and the rotary input element (such as the input shaft of a change-speed transmission, especially a transmission having a plurality of fixed ratios or gears including at least one reverse gear, a neutral gear and several forward gears). A ratio selector member, such as a lever, can be manipulated by the operator of the motor vehicle to select the necessary gear of the transmission. Such power trains are normally further equipped with accelerator pedals which are adjustable to regulate the RPM of the prime mover. The controls for the friction clutch are designed to automatically engage and disengage the clutch, i.e., to disengage the clutch prior to shifting of the transmission into a different gear and to automatically engage the clutch when the shifting into a selected gear is completed.
More specifically, the invention relates to power trains of the type wherein the clutch is operated automatically during the initial stage of operation of the power train, namely while the motor vehicle is being started from zero speed.
European patent No. 0038113 discloses a power train with a clutch control system which is designed to generate an RPM reference signal during starting of the motor vehicle and wherein the engine speed (i.e., the RPM of the rotary output element of the engine) is controlled by engaging the clutch in such a way that the engine speed follows an RPM reference signal. In accordance with the patented invention, the reference RPM is derived from the angle of the pivotable valving element or flap of the throttle valve which regulates the admission of fuel into the engine. The arrangement is such that, when the engine torque increases (i.e., in response to increased rate of fuel admission to the engine), the reference signal is altered in order to correspond (i.e., to be properly related) to the higher speed of the engine. The extent of engagement of the clutch is proportional to the difference between the engine speed and the reference RPM. The extent of engagement of the clutch increases if the difference between the (higher) engine speed and the (lower) reference RPM increases.
European patent No. 0696341 discloses certain modifications of the power train which is disclosed in the aforediscussed European patent No. 0038113. Such modifications take into consideration an increased idling RPM of the engine and the shifting of the transmission into a starting gear when the engine speed is increased (by opening the throttle valve) prior to shifting of the transmission into such.starting gear.
Additional modifications of the power train protected by the European patent No. 0038113 are disclosed in European patent No. 0735957, namely to ensure satisfactory regulation of engagement of the clutch when the motor vehicle is to be started at a low speed of the engine, i.e., when it is necessary to maneuver (operate) the motor vehicle at relatively low speeds of the engine or another suitable prime mover.
The combined teachings of the European patents Nos. 0038113, 0735957 and 0696341 disclose a power train wherein the operation of the clutch is adequately controlled during starting of the motor vehicle if the starting takes place while the throttle valve is open to a relatively small extent (i.e., when the angular position of the flap of the throttle valve is remote from the angular position such flap assumes in the fully open condition of the throttle valve. If the angle of the flap is less than 20% of the angle in the fully open position of the valve, the maximum torque normally develops at engine speeds of less than about 1500 1/min. If the angle is increased above 20% of the maximum angle, e.g., to between 60% and 90%, the engine speed rapidly increases to provide a maximum torque. In presently known power trains, such mode of operation permits for a rapid engagement of the clutch which, however, invariably or frequently entails a choking of the engine. Moreover, even though (under normal circumstances) certain presently known power trains permit for a starting of the motor vehicle from a standstill in a slightly open position of the throttle valve, it is necessary to open the throttle valve to a much greater extent if the vehicle is to be set in motion along a steep road surface and/or while the vehicle carries a substantial load.
International application Serial No. PCT/GB97/03497 (published Jul. 2, 1998) under No. WO 98/28162) discloses a method of determining, during a clutch reengagement stage, the so-called kiss point of the clutch. The latter includes a driven plate which transmits torque from the engine to the wheels by way of a multiple-ratio transmission when the clutch is engaged. The clutch actuating mechanism is controlled by an electronic control unit. The method includes the steps of checking whether or not the throttle valve is closed and the vehicle is in an engine overrun condition, partially reengaging the clutch up to a point where the clutch increases the engine speed to a substantially constant level below the speed of the drive plate, monitoring the position of the clutch actuating mechanism when the clutch is partly engaged, computing on the basis of such condition measurements and the known engagement/torque characteristics of the clutch at the current kiss-point position and completing the engagement of the clutch. The inventors named in the aforementioned U.S. patent state that the object of their invention is to calibrate the clutch and more specifically, to determine xe2x80x9cthe so-called xe2x80x98Kiss-pointxe2x80x99 of a clutch when the clutch just begins to make frictional contact during its engagementxe2x80x9d. The inventors further state that an object of their invention is to provide a method of determining the kiss-point of a clutch which can be regularly implemented during use of the associated vehicle with the minimal effect on the operation of the vehicle so that the determination is not perceived by the operator or passengers.
Commonly owned U.S. Pat. No. 5,176,234 (granted Jan. 5, 1992 to Reik et al. for xe2x80x9cMETHOD OF REGULATING THE OPERATION OF AUTOMATIC CLUTCHESxe2x80x9d) discloses a method of regulating the operation of an automatic friction clutch, which is installed between a prime mover and a transmission in a power train of a motor vehicle, during at least one of various stages of operation including starting, driving, accelerating, braking, driving in reverse and parking of the vehicle and shifting of transmission into different gears as well as during transitions between such stages. The patented method comprises the steps of monitoringxe2x80x94at least for the purpose of starting the vehiclexe2x80x94at least one selected predetermined parameter including measuring the torque in the power train and/or the angular positions of clutch parts while the condition of the clutch is being changed from clutch-open, with the vehicle at a standstill and with the transmission in a gear other than neutral, at a predetermined speed toward clutch-closed to an extent such that the clutch transmits a torque less than that which is required to set the vehicle in motion, determining the clutch-open condition when the transmitted torque and/or the angular positions of clutch parts reach a predetermined value, memorizing such value, thereupon changing the condition of the clutch toward clutch-open, fully opening the clutch in dependency on starting of the engine, thereupon closing the clutch at least until determination of regulation starting point, memorizing the corresponding condition of the clutch, and thereupon reopening the clutch until the clutch reaches a state of readiness.
European patent No. 0 601 728 A1 to Slicker et al. discloses a friction clutch which couples the engine and the gear transmission of a vehicle and is controlled by a microprocessor based circuit using logic which defines operating modes according to engine and clutch conditions. During the time of clutch closure, when the vehicle is starting from rest in a startup or launch mode, the throttle or other engine control signal is restrained from quickly responding to the accelerator pedal. This avoids engine overspeeding which results in generating high torque before sufficient clutch capacity has been achieved. The control signal is developed as a function of the pedal position under control of throttle logic which, in turn, is dependent upon clutch operating modes defined by the clutch logic. The clutch operating modes are four modes for automatic clutch operation comprising touch point approach mode which prohibits a throttle signal during initial clutch movement, creep mode or startup mode after touch point occurs, and lockup mode for completing clutch closing when low clutch slip is attained. A non-automatic mode is entered before the accelerator pedal is depressed or when engine stall conditions are detected.
An object of the present invention is to provide a power train which is superior to presently known power trains under several circumstances such as setting the motor vehicle in motion on a steeply inclined road surface and/or while the vehicle carries a substantial load.
Another object of the invention is to provide a novel and improved control unit or system for the friction clutch which is engageable to transmit torque between a prime mover and a transmission in the power train of a motor vehicle.
A further object of the invention is to provide a novel and improved engine-clutch-transmission combination for use in the power train of a motor vehicle.
An additional object of the instant invention is to provide a motor vehicle which embodies the above outlined power train.
Still another object of the present invention is to provide a power train which exhibits the above outlined features and characteristics and can utilize an automatic clutch actuating device in conjunction with a partially or fully engaged change-speed transmission.
A further object of the invention is to provide an electronic clutch actuating or clutch control unit which employs an electric motor, a pneumatic device or a hydraulic device which serves to select the extent of engagement of the friction clutch in the power train of a motor vehicle.
An additional object of the invention is to provide a novel and improved method of operating the friction clutch between the engine and the transmission in the power train of a motor vehicle, especially preparatory to and during the initial stage or stages of setting a motor vehicle in motion, for example, while the motor vehicle is supported by a steeply inclined surface and/or when the motor vehicle carries a large load.
One feature of the present invention resides in the provision of a power train for use in a motor vehicle. The improved power train comprises a variable-speed prime mover (such as an internal combustion engine) arranged to furnish a plurality of different torques including a maximum torque and having an output element (such as a camshaft or a crankshaft) arranged to rotate at a plurality of different speeds, means for varying the speed of the prime mover including an energy supplying device (such as a throttle valve) which is adjustable between a plurality of positions including a threshold position, a transmission which is selectively shiftable into a neutral gear and a plurality of additional gears (such as at least one reverse gear and one, two, three or more forward gears), means (such as a ratio selecting lever) for shifting the transmission into different gears, a torque transmitting friction clutch which is engageable and disengageable to respectively transmit and interrupt the transmission of torque between the output element of the prime mover and a rotary input element (e.g., a shaft) of the transmission, and control means for the clutch. The control means includes means for disengaging the clutch prior to shifting of the transmission from neutral gear into one of the additional gears preparatory to setting of the vehicle in motion in response to shifting of the transmission into the one additional gear, to subsequent adjustment of the energy supplying device beyond the threshold position and subsequent to partial engagement of the clutch to a condition in which the clutch transmits torque without play in the power train. The control means is arranged to effect a greater engagement of the clutch beyond the partial engagement in response to the establishment of a predetermined difference between an actual speed of the output element of the prime mover and a reference speed; such greater engagement of the clutch results in the transmission of a torque corresponding to that when the speed of the prime mover at least approximates the reference speed regardless of the adjustment of the energy supplying device at the time when the motor vehicle is being set in motion.
The means for adjusting the throttle valve can include an accelerator pedal or the like.
The friction clutch can be of the type wherein at least one pressure plate is driven by the output element of the prime mover and which further includes an output member (such as a clutch disc provided with customary friction linings) which is connected with the input element of the transmission. The establishment of the aforementioned partial engagement of the clutch can include a movement of the at least one pressure plate into frictional engagement with the output member of the clutch, and the control means is or can be further arranged to engage the at least one pressure plate with the driven member of the clutch and to thus establish the aforementioned condition of the clutch when the energy supplying device is adjusted to assume the threshold position. Furthermore, the control means is or can be arranged to engage the clutch with a slip between the at least one plate and the output member of the clutch to an extent such that the torque being then transmitted by the clutch is less than but approximates (such as closely approximates) the maximum torque adapted to be furnished by the prime mover. The reference speed of the output element of the prime mover is or can be a function of the extent of adjustment of the energy supplying device and is selected to ensure that the extent of engagement of the clutch at least approximates the extent which is necessary to ensure that the torque being transmitted by the clutch at least approximates the torque being transmitted by the output element of the prime mover. The reference speed can be derived by subtracting a function depending upon the position of the energy supplying device from an initial speed of the prime mover. For example, the reference speed can be derived from an initial prime mover speed by subtracting from the initial prime mover speed a constant and a first function dependent upon the position of the energy supplying device and by addingxe2x80x94at positions of the energy supplying device beyond a threshold positionxe2x80x94a second function dependent upon the position of the energy supplying device. The reference speed is or can be maintained at a maximum value at least in one position of the energy supplying device beyond a second threshold position. The just mentioned maximum value of the reference speed can be at most 1000 RPM (often at most 500 RPM) above an idling speed of the prime mover.
In accordance with one presently preferred embodiment of the invention, the reference speed is a function of the position of the energy supplying device, of the selected gear of the transmission and the speed of the motor vehicle, and such reference speed can be derived or ascertained by resorting to the equation
RREF=f(xcex1, gear, vehicle speed)
wherein RREF is the reference speed, xcex1 is the angular position of the flap or another suitable pivotable member of the throttle valve or another suitable energy supplying device expressed as a percentage of full travel of the pivotable member, xe2x80x9cgearxe2x80x9d is the gear selected by the shifting means, and xe2x80x9cvehicle speedxe2x80x9d is self-explanatory.
The reference speed can be further derived in dependency upon buffer means. The rate of change of the reference speed with changes of angular position of the pivotable member can be matched with changes of speed of the prime mover in response to changes of position of the pivotable member. Such power train can further comprise a low pass filter for the reference speed to establish a dynamic correspondence between the reference speed and the speed of the prime mover. The characteristics of the low pass filter can vary with shifting of the transmission into selected gears and as a function of variations of at least one of (a) the speed of the prime mover, (b) the speed of the input element of the transmission, and (c) the speed of the motor vehicle. The initial value of the output of the low pass filter can at least substantially match the speed of the prime mover. Furthermore, the output of the low pass filter can converge upon the value of the reference speed as determined by the position of the energy supplying device.
In deriving the reference speed from an initial speed of the prime mover, the initial speed is or can be reduced exponentially toward an idling speed of the prime mover.
In accordance with a further modification, the reference speed can be arrived at in accordance with the equation
RREF=RINTxe2x88x92Kxe2x88x92K1+K2(xcex1xe2x88x92xcex1T)2
wherein RINT is an initial speed of the prime mover, K is a first constant, K1 is a second constant, K2 is a third constant, xcex1 is the angular position of a pivotable member of the energy supplying device expressed as a percentage of full travel of the pivotable member, xcex1T is a threshold angle of the pivotable member expressed as a percentage of full travel of the pivotable member, and K2(xcex1xe2x88x92xcex1T)2 is applicable only when xcex1 greater than xcex1T.
The value of xcex1T is or can be between 40% and 60% of full travel of the pivotable member of the energy supplying device, and the values of the aforementioned constants K, K1 and K2 are or can be dependent upon the selection of the gear of the transmission.
Another feature of the present invention resides in the provision of a clutch control system for the automatic control of an engageable and disengageable clutch in a motor vehicle wherein the clutch connects an engine with a gearbox and the gearbox has a plurality of fixed ratios and a neutral ratio as well as selector means by which the neutral ratio and any one of the fixed ratios can be selected. The motor vehicle is provided with a throttle and with a throttle control for controlling the speed of the aforesaid engine. The clutch control system automatically controls the engagement and disengagement of the clutch to permit changes of the gear ratio and the clutch control system is arranged to permit take-up from disengagement of the clutch to be initiated upon selection of the takeup gear. Subsequent opening of the throttle control beyond a threshold value causes the clutch to be engaged to a point at which any lost motion in a power train between the engine and the gearbox is subsequently taken up. Further engagement of the clutch depends upon the difference between the actual speed and a reference speed of the engine, and the reference speed can be derived in such a way that the difference between the actual speed and the reference speed establishes an extent of clutch engagement which permits for the transmission of torque that is substantially equal to torque being furnished by the engine at the actual engine speed over the full range of throttle openings encountered during takeup from rest position.
A further feature of the invention resides in the provision of methods of operating the clutch in the power train of a motor vehicle in a manner as pointed out herein-before, as pointed out in the following detailed description of the drawings and as pointed out in the appended claims.
The novel features which are considered as characteristic of the invention are set forth in particular in the appended claims. The improved power train itself, however, both as to its construction and the modes of assembling and operating the same, together with numerous additional important and advantageous features and attributes thereof, will be best understood upon perusal of the following detailed description of certain presently preferred specific embodiments with reference to the accompanying drawings.